Blank for a flow forming method

ABSTRACT

There is disclosed a tubular blank (31) for attaching to a stepped mandrel (41) of a flow forming assembly, wherein the tubular blank (31) has a stepped inner profile that may be tailored to the shape of the mandrel (41) before any flow forming is carried out on the blank (31). Also disclosed is a corresponding method of flow forming a shaped article by plastically deforming the tubular blank (31) over the stepped mandrel (41), where the forming of the shaped article may be carried out in one operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure claims the benefit of UK Patent Application No. GB1818468.9, filed on 13 Nov. 2018, which is hereby incorporated herein inits entirety.

TECHNICAL FIELD

The present disclosure concerns a blank to be used in a flow formingmethod to produce a shaped article. The present disclosure also concernsa method of flow forming a shaped article using the blank.

BACKGROUND

Flow forming is a known metal forming process (sometimes known as a“chip-less machining method”) for producing a shaped article from ablank using a cold rolling process. The shaped articles to be producedare typically in the form of rotationally symmetric, cylindricalcomponents for aerospace applications, including undercarriagecomponents, hydraulic cylinders and drive shafts for gas turbineengines.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described by way of example only, with referenceto the Figures, in which:

FIG. 1 is a schematic illustration of a known flow forming method;

FIG. 2 is a sectional side view of a gas turbine engine;

FIG. 3 schematically illustrates a blank and corresponding mandrel to beused in a flow forming method according to the present disclosure;

FIG. 4 schematically illustrates the blank of FIG. 3 in detail; and

FIG. 5 schematically illustrates a method of producing a shaped articleby flow forming the blank of FIGS. 3 and 4, in accordance with thepresent disclosure.

DETAILED DESCRIPTION

FIG. 1 shows a typical flow forming assembly 1. The assembly 1 comprisesforming rollers 2 configured to plastically deform a blank in the formof an initial machined generally tubular pre-form 3 over a mandrel 4 tocreate a shaped article. The blank 3 is fitted tightly to the mandrel 4such that when the mandrel 4 rotates, so does the blank 3. The rollers 2move over the blank 3 along a mandrel axis X and rotate when in contactwith the blank 3. As the mandrel 4 and rollers 2 rotate, and the rollers2 are moved against the blank 3 towards a tailstock 5 of the mandrel 4,the blank is plastically deformed, such that the blank 3 is elongatedand the walls of the tubular blank 3 are thinned, to produce a shapedarticle.

Typically, the wall thickness of the flow formed sections of the tubularblank 3 is reduced between a minimum of 20% and a maximum of 80% duringa flow forming pass, which enables modest changes to the outer diameterto provide contour changes on the outer profile that cannot be achievedby alternative processes such as extrusion or drawing. Reducing the wallthickness consequently elongates the pre-form along the longitudinalaxis X of the mandrel 4, such that the shaped article will have an innerdiameter that matches the diameter of the mandrel 4. Typical elongationsrange between 100 and 400% of the original length of the blank.

Although flow forming is typically used to manufacture a shaped articlehaving a single inner diameter, there are some applications where it isnecessary or desired for the shaped article to have two inner diameters.Accordingly, it is known to provide a stepped mandrel having two outerdiameters, to be used during the flow forming process. A tubular blankwith a single inner diameter corresponding to the largest mandreldiameter is then fixed over the largest diameter region of the mandrel.The rollers then move over the blank along the mandrel axis toplastically deform the blank such that it forms a shaped article havingtwo inner diameters that should match the shape of the mandrel along itsaxis.

Flow forming an oversized blank across the stepped region of a mandrelfrom the larger diameter region and the smaller diameter region is knownas “necking in” the blank. However, it is often difficult to “neck-in”blanks to accurately match the outer profile of the mandrel. This isparticularly true for higher strength materials that are suitable foraerospace applications. Indeed, necking in has limitations in terms ofthe material type (strength) and thickness to be used for the blank, aswell as the resulting length of the shaped article and the extent ofvariation between the inner diameters that is able to be achieved forthe shaped article.

Accordingly, it is desired to provide an improved blank andcorresponding flow forming method.

According to a first aspect of the disclosure there is provided atubular blank for attaching to a stepped mandrel of a flow formingassembly, wherein the tubular blank has a stepped inner profile.

In other words, the inner profile of the blank is tailored to the shapeof the mandrel (and accordingly the desired inner profile of the shapedarticle) before any flow forming is carried out on the blank.Accordingly, radial flow to conform to the stepped profile of a mandrelis reduced as compared with radial flow when using an un-stepped tubularblank. That is, the radial extent by which the inner surface(s) of theblank must deform to conform to the mandrel is reduced. In examples, theradial extent by which the inner surface(s) of the blank must deform toconform to the mandrel is less than the radial extent of a step in theinner profile of the blank.

In this way, the blank will conform to the shape of the stepped mandrelmore closely during flow forming, such that the resultant shaped articlewill have an inner profile that more accurately matches the outerprofile of the mandrel, as compared to, e.g., conventional arrangementsin which an oversized blank is “necked-in”.

The stepped inner profile may comprise a first inner surface extendingcircumferentially about a central longitudinal axis to define a firstinner volume having a first inner diameter. The stepped inner profilemay comprise a second inner surface axially adjacent the first innersurface and extending circumferentially about the central longitudinalaxis to define a second inner volume having a second inner diameter thatis larger than the first inner diameter. The stepped inner profile maycomprise an inner shoulder between the first inner surface and thesecond inner surface.

The first inner surface and the second inner surface may be parallel toa central longitudinal axis of the blank to define a substantiallycylindrical first inner volume and a substantially cylindrical secondinner volume, respectively. The first inner surface and the second innersurface may, however, be angled with respect to the central longitudinalaxis, such that the first inner volume and the second inner volume aretapered in the longitudinal direction. In that case, the first innerdiameter may correspond to an inner diameter of the first inner volume,and the second inner diameter may correspond to an inner diameter of thesecond inner volume.

The tubular blank may comprise an end wall extending radially inwardlyfrom the second inner surface to at least partly close the first innervolume. The end wall may be a flange.

The tubular blank may be made of a material comprising at least one of awrought steel, a nickel alloy and a titanium alloy.

According to a second aspect of the disclosure there is provided a flowforming kit comprising a stepped mandrel and a tubular blank accordingto any one or more of the statements above.

The stepped mandrel may comprise a first mandrel region having a firstouter mandrel diameter and a second mandrel region having a largersecond outer mandrel diameter. The tubular blank may be configured tocooperate with the stepped mandrel in that the first inner diametercorresponds to, e.g. matches, the first outer mandrel diameter such thatthe first inner volume is suitable for, e.g. snugly, receiving the firstmandrel region. The tubular blank may be configured to cooperate withthe stepped mandrel in that the second inner diameter corresponds to,e.g. matches, the second outer mandrel diameter such that the secondinner volume is suitable for, e.g. snugly, receiving the second mandrelregion.

The first inner volume and the first mandrel region may have anengineering fit, preferably a location or transition fit. The secondinner volume and the second mandrel region may have an engineering fit,preferably a location or transition fit.

The first inner surface may have an axial extent such that, when thefirst inner volume receives the first mandrel region, an inner shoulderof the blank longitudinally opposes an outer mandrel shoulder betweenthe first mandrel region and the second mandrel region.

The first inner surface may have an axial extent such that, when thefirst inner volume is fully occupied by the first mandrel region, somebut not all of the second mandrel region is received by the second innervolume of the blank, to support the blank on the second mandrel region.

A step of the inner profile may have a shape that conforms to the shapeof a step in the mandrel. The inner shoulder of the blank may beparallel with the outer mandrel shoulder, when the first inner volumereceives the first mandrel region.

The present disclosure extends to a method of flow forming a shapedarticle using a stepped mandrel and a tubular blank as described abovein accordance with any one of the statements included herein.

Thus, according to a third aspect of the disclosure, there is provided amethod of flow forming a shaped article, comprising: providing a steppedmandrel that comprises a first mandrel region having a first outermandrel diameter and a second mandrel region having a second outermandrel diameter that is larger than the first outer mandrel diameter;providing a tubular blank having a stepped inner profile; locating thetubular blank on the mandrel; and plastically deforming the tubularblank over the mandrel to create the shaped article.

The tubular blank may comprise a first inner volume having a first innerdiameter and a second inner volume having a second inner diameter thatis larger than the first inner diameter. Locating the tubular blank onthe mandrel may comprise the tubular blank snugly receiving the firstmandrel region in the first inner volume of the tubular blank.

The method may comprise locating the tubular blank on the mandrel suchthat an inner shoulder of the blank longitudinally opposes an outershoulder of the mandrel. The method may also comprise plasticallydeforming the tubular blank over the mandrel such that the innershoulder of the blank translates longitudinally along the first mandrelregion towards the outer shoulder of the mandrel.

The method may comprise one or more rollers engaging a first outersurface of the blank, which is radially outwards of a first innersurface defining the first inner volume, thereby elongating the firstinner surface such that the inner shoulder translates longitudinallyalong the first mandrel region towards the outer shoulder of themandrel. The method may comprise the one or more rollers disengaging thefirst outer surface in response to determining that the inner shoulderof the blank is abutting the outer mandrel shoulder. The method maycomprise the one or more rollers engaging a second outer surface of theblank, which is radially outwards of a second inner surface defining thesecond inner volume, thereby elongating the second inner surface alongthe second mandrel region while keeping the inner shoulder of the blankin an abutting arrangement with the outer mandrel shoulder.

Longitudinal translation of the inner shoulder along the first mandrelregion may cause the second inner volume of the blank to translate inthe same longitudinal direction such that it snugly receives the secondmandrel region.

Plastically deforming the tubular blank over the mandrel to create theshaped article may comprise elongating the tubular blank without, e.g.substantially, changing the inner diameters of the tubular blank duringthe flow forming method. However, it will be appreciated that there maybe a slight diametric change of the inner diameters of the blank duringflow forming as a result of slight tangential flow of material.

The forming of the shaped article may be carried out in one operation.

The skilled person will appreciate that except where mutually exclusive,a feature described in relation to any one of the above aspects may beapplied mutatis mutandis to any other aspect. Furthermore except wheremutually exclusive any feature described herein may be applied to anyaspect and/or combined with any other feature described herein.

With reference to FIG. 2, a gas turbine engine is generally indicated at10, having a principal and rotational axis 11. The engine 10 comprises,in axial flow series, an air intake 12, a propulsive fan 13, anintermediate pressure compressor 14, a high-pressure compressor 15,combustion equipment 16, a high-pressure turbine 17, an intermediatepressure turbine 18, a low-pressure turbine 19 and an exhaust nozzle 20.A nacelle 21 generally surrounds the engine 10 and defines both theintake 12 and the exhaust nozzle 20.

The gas turbine engine 10 works in the conventional manner so that airentering the intake 12 is accelerated by the fan 13 to produce two airflows: a first air flow into the intermediate pressure compressor 14 anda second air flow which passes through a bypass duct 22 to providepropulsive thrust. The intermediate pressure compressor 14 compressesthe air flow directed into it before delivering that air to the highpressure compressor 15 where further compression takes place.

The compressed air exhausted from the high-pressure compressor 15 isdirected into the combustion equipment 16 where it is mixed with fueland the mixture combusted. The resultant hot combustion products thenexpand through, and thereby drive the high, intermediate andlow-pressure turbines 17, 18, 19 before being exhausted through thenozzle 20 to provide additional propulsive thrust. The high 17,intermediate 18 and low 19 pressure turbines drive respectively the highpressure compressor 15, intermediate pressure compressor 14 and fan 13,each by suitable interconnecting shaft.

Other gas turbine engines to which the present disclosure may be appliedmay have alternative configurations. By way of example such engines mayhave an alternative number of interconnecting shafts (e.g. two) and/oran alternative number of compressors and/or turbines. Further the enginemay comprise a gearbox provided in the drive train from a turbine to acompressor and/or fan.

The shafts used in gas turbine engines, such as the interconnectingshafts of FIG. 2, are rotationally symmetric, cylindrical componentsthat transfer torque between different parts of the engine. The shaftsoften traverse large sections of the engine and in regions where spacemay be limited, e.g. due to the presence of other components. It istherefore necessary, on occasions, for a shaft to be manufactured withvarying inner diameters, e.g. to reduce the overall size of one or moreregions of the shaft or to connect the shaft to correspondingly sizedcomponents of the engine. Furthermore, the shaft is often tapered tofacilitate or ease assembly when feeding the shaft into the core of theengine. The tapered nature also contributes to the stiffness of thecomponent.

With reference to FIGS. 3 and 4, there is described a flow forming kitcomprising a blank 31 and corresponding stepped mandrel 41, which are tobe used during a flow forming method to manufacture a shaped articlehaving two different inner diameters. FIG. 3 shows a longitudinalcross-section of both the blank 31 and the mandrel 41 when disposedconcentrically about a common central longitudinal axis 50. FIG. 4,meanwhile, shows a more detailed view of the blank 31 of FIG. 3.Although not shown, the blank 31 and the mandrel 41 are eachrotationally symmetric about the longitudinal axis 50, such that theblank 31 and mandrel 41 have generally the same profile as that shown inFIGS. 3 and 4 for any longitudinal cross-section taken along throughaxis 50.

As best shown in FIG. 3, the mandrel 41 is a shaped solid bar, e.g. ofmetal, which is to be placed inside a blank 31 to be flow formed. Themandrel 41 comprises a tailstock 46 which is connected to a lathe (notshown) that, during operation, rotates the mandrel 41 and blank 31 (whenfitted) about the central longitudinal axis 50.

The mandrel 41 is shaped in that it has an outer profile that ispre-configured and machined to match the inner profile that is requiredfor the shaped article to be flow formed. In the example of FIG. 3, themandrel 41 is shaped to define two concentric and axially adjacentcylinders of different diameters. In particular, the mandrel 41comprises a first mandrel region 42 at a distal end from the tailstock46 and a second mandrel region 43 proximal to the tailstock 46 (ascompared to the first mandrel region 43). The first mandrel region 42has a first radially outer surface 421 defining a first outer mandreldiameter 44 and the second mandrel region 43 has a second radially outersurface 431 defining a second outer mandrel diameter 45 that is largerthan the first outer diameter 44.

Between the first radially outer surface 421 and the second radiallyouter surface 431 is a radially extending, outer mandrel shoulder 47. Inthis example, the outer mandrel shoulder 47 is annular, although inother examples it may be tapered in the longitudinal direction, i.e. atan angle relative to axis 50. Surfaces 421, 431, 47 together define astepped profile around the circumference of the mandrel 41.

The values of the first outer diameter 44 and the second outer diameter43, as well as the shape of the outer mandrel shoulder 47 is selected todefine an outer profile that matches the inner profile that the shapedarticle to be flow formed should have. This may involve reverseengineering a notional, predefined shaped article to be manufactured, oran existing shaped article that has been previously manufactured, e.g.,using other manufacturing methods.

While it is known to provide a tubular blank having a single innerdiameter that matches the largest diameter of a stepped mandrel, i.e.the second outer diameter of the mandrel 41 of FIG. 3, it is difficultto flow form such a blank without having to compromise on the accuracy,strength and/or rigidity of the resulting shaped article. However, thepresent disclosure is concerned with a blank 31 that is tailored to theshape of the mandrel 41 (and accordingly the desired inner profile ofthe shaped article) before any flow forming is carried out on the blank31. In particular, the blank of the present disclosure comprises astepped inner profile. The features of the blank 31 of the presentdisclosure will now be described with particular reference to FIG. 4.

The blank 31 is substantially tubular in structure in that it comprisesa wall that extends circumferentially around the longitudinal centralaxis 50 to define a generally cylindrical shape having a hollow centralpassage extending there through in the longitudinal direction. The wallthicknesses are selected so that the corresponding reductions duringflow forming will meet the required wall dimensions for the shapedarticle. The volume of material required is also calculated and selectedaccordingly.

The length of the blank 31 on its radially outer side is divided intotwo axially adjacent sections, a first section comprising a first outersurface 311 that extends along a first length of the blank 31 and asecond section comprising a second outer surface 313 that extends alonga second length of the blank 31. The first and second outer surfaces311, 313 are parallel but separated in the radial direction by an outershoulder 315 that extends radially therebetween.

At longitudinally opposite ends of the blank 31, there is a front endsurface 313 and a rear end surface 314. The rear end surface 314 has afirst opening 38 for receiving the mandrel 41 within the blank 31 andthe front end surface 313 has a second opening 39 such that, when themandrel 41 is received in the first opening 38, the second opening 39allows air to escape the blank 31.

The inner profile of the blank 31 is defined by a first inner surface32, a second inner surface 33, an inner shoulder 36 and an end wallsurface 310. The first inner surface 32 and the second inner surface 33are axially adjacent to one another and both extend parallel to thelongitudinal axis 50 of the blank 31. The inner shoulder 36 and the endwall surface 310 extend radially to the central axis 50. In that way,the inner shoulder 36 and the end wall surface 310 are annular.

The end wall surface 310 extends radially inwardly from the first innersurface 32 to define, together with the front surface 313, an end wallor flange 37 that at least partly closes the first inner volume 316. Theend wall surface 310 is configured to abut the distal end 48 of themandrel 41 that is to be received in the blank 31, in use. In this way,the flange 47 acts as a stopper to prevent the further passage of distalend 48 of the mandrel 41 through the blank 31. The end wall surface 310extends from the first inner surface 32 by a length that ensures thatthe first opening 38 has a diameter that is smaller than the first outerdiameter 44 of the mandrel 41 to be received in the blank 31.

The flange 37 also acts to prevent the mandrel 41 from being inserted inthe blank 31 at the distal end opposite the first opening 38, therebyensuring that the mandrel 41 can only be inserted into the blank 31though the first opening 38 and therefore in the correct orientation forflow forming. The flange may be used to secure the blank 31 to a distalend 48 of the mandrel 41, e.g. using a clamp.

The first inner surface 32 extends circumferentially about the centrallongitudinal axis 50 to define a cylindrical first inner volume 316 ofthe blank 31 and the second inner surface 33 extends circumferentiallyabout axis 50 to define a cylindrical second inner volume 317 of theblank 31.

As mentioned above, the inner profile of the blank 31 is tailored to theshape, i.e. the outer profile, of the mandrel 41 and accordingly, theinner profile that the shaped article is to have after flow forming theblank 31. More specifically, the blank 31 is configured with a steppedinner profile. In this way, the blank 31 will conform to the shape ofthe mandrel more closely during the flow forming method, such that theresultant shaped article will have an inner profile that more accuratelymatches the outer profile of the mandrel 41, as compared to, e.g.,conventional arrangements in which an oversized blank is “necked-in”.

With particular reference to FIG. 4, the first inner volume 316 has afirst inner diameter 34 and the second inner volume 317 has a secondinner diameter 35 which is larger than the first inner diameter 34.Further, the blank 31 is precision engineered such that the first innerdiameter 34 and the second inner diameter 35 are the same as the firstouter diameter 44 and the second outer mandrel diameter 45 of themandrel 41, respectively. That is, the first inner diameter 34 matches(e.g. equals) the first outer mandrel diameter 44 to provide a snug fitbetween the first inner surface 32 and the first radially outer surface421 of the mandrel 41, when the first mandrel region 42 is received inthe first inner volume 316. The second inner diameter 35 matches (e.g.equals) the second outer mandrel diameter 45 to provide a snug fitbetween the second inner surface 33 and the second radially outersurface 431 of the mandrel 41, when the second mandrel region 43 isreceived in the second inner volume 317 (e.g. due to elongation of theblank 31 during flow forming).

Precision engineering the first inner diameter 34 and the second innerdiameter 35 to match the diameters of the mandrel, before the flowforming process, ensures that the inner diameters of the shaped articlewill be closer to the nominal inner diameter values predefined for theshaped article. It will also ensure that regions of the shaped articlethat have different diameters will be concentric, which in turnincreases the integrity of the shaped articles compared to hypotheticalarrangements where concentricity will depend on how accurately therollers can deform the blank to fit the mandrel.

The inner profile of the blank 31 is also tailored to the shape of themandrel 41 in that the stepped profile itself corresponds to, e.g.closely matches or conforms to, the shape of the stepped profile of themandrel. In particular, the inner shoulder 36 of the blank 31 isparallel with the outer mandrel shoulder 47, when the blank 31 islocated on the mandrel 41.

It will be appreciated that, although the mandrel 41 and correspondingblank 31 are shown in the Figures to have only two regions or volumeshaving different diameters, the mandrel 41 and corresponding blank 31may be machined to include any number of inner volumes having differentrespective diameters, as desired.

It is also not necessary for the inner shoulder 36 to be annular, i.e.perpendicular to the first inner surface 32 and the second inner surface33 of the blank 31. The inner shoulder 36 can be of any desired shape,and be disposed with any orientation relative to the first inner surface32 and the second inner surface 33 of the blank 31. For example, theinner shoulder 36 may be a curved surface, or may be a planar surfacethat is angled relative to the first inner surface 32 and the secondinner surface 33 of the blank 31. The configuration of the innershoulder 36 will depend, in embodiments, on the shape and orientation ofthe outer shoulder 47 machined into the mandrel 41.

The blank 31 can be manufactured from e.g. a bar, a forging, a tube,welded wrapper or by extrusion. Furthermore, the blank 31 may comprisematerials typically considered to be too hard or rigid to be flow formedonto a stepped mandrel with sufficient accuracy. Such materials include,for example, wrought steels, nickel (super-)alloys and titanium alloysor generally medium alloy steels. In particular, the tubular blank maybe made of any one of IN718, C263, CMV, 17/4PH, and A286 alloys, etc.

In use a flow forming method is carried out on the blank 31, whererollers are configured to plastically deform the blank 31 over themandrel 41, to create a shaped article. The flow forming method of thepresent disclosure will now be described in detail with respect to FIGS.5a -5 c.

The method begins as shown in FIG. 5a by locating the tubular blank 31to the mandrel 41. The mandrel 41 is inserted into the blank 31 viafirst opening 38 such that the inner shoulder 36 of the blank 31longitudinally opposes the outer mandrel shoulder 47. The distal end 48of the mandrel 41 is received in the blank 31 and abuts the end wallsurface 310. The blank 31 is then secured to the mandrel 41 such thatthe blank 31 will rotate together with the mandrel 41 during the flowforming method.

The tubular blank 31 snugly receives the first mandrel region 42 in thefirst inner volume 316, such that the first inner surface 32 sheathessome but not all of the length of the first mandrel region 42 of themandrel 41. This is in contrast to conventional flow forming methodswhere the entire blank is located about the outside of the largestdiameter region of the mandrel, i.e. corresponding to the second mandrelregion 43 of FIG. 3.

The blank 31 is also configured, e.g. in length, such that when it issecured to the mandrel 41, a portion (some, but not all) of the secondinner surface 33 is in contact with and sheathes some, but not all ofthe length of the second mandrel region 43. That is, an axial extent ofthe first inner volume 316 and an axial extent of the second innervolume 317 are configured such that, when the first inner volume 316 isfully occupied by the first mandrel region 42, some but not all of thesecond mandrel region 43 is received by the second inner volume 317 ofthe blank 31. In this way, the blank 31 is supported on the secondmandrel region 43 during the flow forming method. This increases thestability of the blank 31 and acts to guide the blank along the mandrel41 as the blank 31 is elongated.

As shown in FIG. 5b , the rollers engage the first outer surface 311 ofthe blank 31 while it is under rotation and translate in a longitudinaldirection towards the tailstock 46, such that the outer wall of theblank 31 thins and elongates along the radially outer surface 421. Thatis, the rollers first engage the blank 31 in a region corresponding tothe smallest mandrel diameter and translate along the blank 31 in thelongitudinal direction towards a region corresponding to the largestmandrel diameter. This is in contrast to hypothetical flow formingmethods where the rollers translate in a direction beginning at thelargest mandrel diameter and towards the smallest mandrel diameter.

The inner shoulder 36 of the blank 31 is caused to translatelongitudinally along the first mandrel region 42 towards the outershoulder 47 of the mandrel 41. The longitudinal translation of the innershoulder 36 along the first mandrel region 42 causes the second innervolume 317 of the blank 31 to translate in the same longitudinaldirection such that it snugly receives the second mandrel region 43.This will continue until it is determined that the inner shoulder 36 ofthe blank 31 abuts or contacts the outer mandrel shoulder 47 machinedinto the mandrel 41, in response to which the rollers radially retractand disengage the blank 31 as denoted by arrow 52 in FIG. 5b , toprevent further thinning.

The flow forming method proceeds as shown in FIG. 5c , where the rollersrelocate and re-engage the blank 31 on the second outer surface 312 andtranslate in a longitudinal direction towards the tailstock 46, untilthe second inner surface 33 is elongated to a desired length, whilekeeping the inner shoulder 36 of the blank 31 in an abutting arrangementwith the outer mandrel shoulder 47. The resulting shaped article 51 isthen detached from the mandrel and the flange 37 may be removed ifdesired.

The shaped article 51 is in the form of a shaft having an inner profilethat comprises two inner diameters that are equal to the first andsecond outer diameters of the mandrel 41. However, it will beappreciated that the inner diameters will substantially correspond tothe first inner diameter and the second inner diameter of the originalblank, such that the inner diameters of the blank remain unchangedduring the flow forming method. The outer profile of the shaped articlemay vary from that shown in FIG. 5 to include provide contour changes,as desired.

The blank 31 is flow formed to produce the completed shaped article 51in a single operation in which the blank 31 remains secured to themandrel 41, i.e. the blank 31 is not removed from the mandrel 41 untilafter completion of the flow forming method. This reduces the complexity(the number of additional operations, set up and cost) of the flowforming method as compared to hypothetical methods in which flow formingis paused so that a blank can be removed from the mandrel, e.g. tomachine a second inner diameter into the blank, before resuming the flowforming operation.

From the above, it is clear that the technology described hereinfacilitates the production of a more accurate shaped article in that thefinal inner diameters will be closer to the nominal predefined valuesfor the shaped article, thereby improving general tolerances of theshaped article due to the inherent stability associated with forming aclosely matched article against a mandrel. It also enables materials ofhigher strength, and blanks of greater thicknesses, to be used to flowform a shaped article, thereby increasing the versatility of the flowforming method.

It will be understood that the invention is not limited to theembodiments above-described and various modifications and improvementscan be made without departing from the concepts described herein. Exceptwhere mutually exclusive, any of the features may be employed separatelyor in combination with any other features and the disclosure extends toand includes all combinations and sub-combinations of one or morefeatures described herein.

What is claimed is:
 1. A tubular blank (31) for attaching to a steppedmandrel (41) of a flow forming assembly, wherein the tubular blank (31)has a stepped inner profile.
 2. The tubular blank (31) as claimed inclaim 1, wherein the tubular blank (31) has a stepped inner profilecomprising: a first inner surface (32) extending circumferentially abouta central longitudinal axis (50) to define a first inner volume (316)having a first inner diameter (34); a second inner surface (33) axiallyadjacent the first inner surface (32) and extending circumferentiallyabout the central longitudinal axis (50) to define a second inner volume(317) having a second inner diameter (35) that is larger than the firstinner diameter (34); and an inner shoulder (36) between the first innersurface (32) and the second inner surface (33).
 3. The tubular blank(31) as claimed in claim 2, further comprising an end wall (37)extending radially inwardly from the second inner surface (33) to atleast partly close the first inner volume (316).
 4. The tubular blank(31) as claimed in claim 1, wherein the tubular blank (31) is made of amaterial comprising at least one of a wrought steel, a nickel alloy anda titanium alloy.
 5. A flow forming kit comprising: a stepped mandrel(41) comprising a first mandrel region (42) having a first outer mandreldiameter (44) and a second mandrel region (43) having a larger secondouter mandrel diameter (45); and a tubular blank (31) as claimed inclaim 2; wherein the tubular blank (31) is configured to cooperate withthe stepped mandrel in that: the first inner diameter (34) correspondsto the first outer mandrel diameter (44) such that the first innervolume (316) is suitable for receiving the first mandrel region (42);and the second inner diameter (35) corresponds to the second outermandrel diameter (45) such that the second inner volume (317) issuitable for receiving the second mandrel region (43).
 6. The flowforming kit as claimed in claim 5, wherein: the first inner surface (32)has an axial extent such that, when the first inner volume (316)receives the first mandrel region (42), an inner shoulder (36) of theblank (31) longitudinally opposes an outer mandrel shoulder (47) betweenthe first mandrel region (42) and the second mandrel region (43).
 7. Theflow forming kit as claimed in claim 5, wherein: the first inner surface(32) has an axial extent such that, when the first inner volume (316) isfully occupied by the first mandrel region (42), some but not all of thesecond mandrel region (43) is received by the second inner volume (317)of the blank (31), to support the blank (31) on the second mandrelregion (43).
 8. The flow forming kit as claimed in claim 5, wherein astep of the inner profile has a shape that conforms to the shape of astep in the mandrel (41).
 9. A method of flow forming a shaped article(51), comprising: providing a stepped mandrel (41) that comprises afirst mandrel region (42) having a first outer mandrel diameter (44) anda second mandrel region (43) having a second outer mandrel diameter (45)that is larger than the first outer mandrel diameter (44); providing atubular blank (31) having a stepped inner profile; locating the tubularblank (31) on the mandrel (41); and plastically deforming the tubularblank (31) over the mandrel (41) to create the shaped article (51). 10.The method of flow forming a shaped article (51) as claimed in claim 9,wherein: the tubular blank (31) comprises a first inner volume (316)having a first inner diameter (34) and a second inner volume (317)having a second inner diameter (35) that is larger than the first innerdiameter (34); and locating the tubular blank (31) on the mandrel (41)comprises the tubular blank (31) snugly receiving the first mandrelregion (42) in the first inner volume (316) of the tubular blank (31).11. The method of flow forming a shaped article (51) as claimed in claim10, comprising: locating the tubular blank (31) on the mandrel (41) suchthat an inner shoulder (36) of the blank (31) longitudinally opposes anouter shoulder (47) of the mandrel (41); and plastically deforming thetubular blank (31) over the mandrel (41) such that the inner shoulder(36) of the blank (31) translates longitudinally along the first mandrelregion (42) towards the outer shoulder (47) of the mandrel (41).
 12. Themethod of flow forming a shaped article (51) as claimed in claim 11,further comprising: one or more rollers engaging a first outer surface(311) of the blank (31), which is radially outwards of a first innersurface (32) defining the first inner volume (316), thereby elongatingthe first inner surface (32) such that the inner shoulder (36)translates longitudinally along the first mandrel region (42) towardsthe outer shoulder (47) of the mandrel (41); the one or more rollersdisengaging the first outer surface (311) in response to determiningthat the inner shoulder (36) of the blank (31) is abutting the outermandrel shoulder (47); and the one or more rollers engaging a secondouter surface (312) of the blank (31), which is radially outwards of asecond inner surface (33) defining the second inner volume (317),thereby elongating the second inner surface (33) along the secondmandrel region (43) while keeping the inner shoulder (36) of the blank(31) in an abutting arrangement with the outer mandrel shoulder (47).13. The method of flow forming a shaped article (51) as claimed in claim11, wherein longitudinal translation of the inner shoulder (36) alongthe first mandrel region (42) causes the second inner volume (317) ofthe blank (31) to translate in the same longitudinal direction such thatit snugly receives the second mandrel region (43).
 14. The method offlow forming a shaped article (51) as claimed claim 9, whereinplastically deforming the tubular blank (31) over the mandrel (41) tocreate the shaped article (51) comprises elongating the tubular blank(31) without changing the inner diameters of the tubular blank (31)during the flow forming method.